class_docstr: Class for the Hitting Set Algorithm to obtain a approximate minimal set of backdoor variables
  to condition on for each node pair.
docstr: Find approximate minimal set of nodes such that there is atleast one node from each set in list_of_sets.
  
  :returns: Approximate minimal set of nodes.
docstr_tok: ["Find","approximate","minimal","set","of","nodes","such","that","there","is","atleast","one","node","from","each","set","in","list_of_sets",".",":","returns",":","Approximate","minimal","set","of","nodes","."]
code: def find_set(self):
      """
      Find approximate minimal set of nodes such that there is atleast one node from each set in list_of_sets.
  
      :returns: Approximate minimal set of nodes.
      """
      var_set = set()
      num_indices = len(self._list_of_sets)
      indices_covered = set()
      all_set_indices = set([i for i in range(num_indices)])
  
      while not self._is_covered(indices_covered, num_indices):
          set_index = all_set_indices - indices_covered
          max_el = self._max_occurence_var(var_dict=self._var_count)
          if max_el is None:
              break
          var_set.add(max_el)
  
          # Modify variable count and indices covered
          covered_present = self._indices_covered(
              el=max_el, set_index=set_index
          )
          self._modify_count(covered_present)
          indices_covered = indices_covered.union(covered_present)
      return var_set
  
imports: import networkx
  from dowhy.utils.graph_operations import adjacency_matrix_to_adjacency_list
label_desc: Use image node_id 3 for calling the HittingSetAlgorithm obj's underlying member method code with example usage: obj.find_set() and returns: var_set